engleski

Applicability of the Paste Electrolyte Cell for Detection of Protective Layers on Bronze

A common method of protecting bronze artefacts is to use a protective coating on natural and artificial patina. Various electrochemical techniques can be used to evaluate the effect of a treatment, to select the most appropriate coating, or to know when a coating needs to be renewed. Electrochemical impedance spectroscopy (EIS) as a tool for quantifying the protective properties of protective layers exposed to a variety of corrosive environments, from controlled conditions in museums to highly corrosive conditions outdoors, offers great potential for evaluating the state of preservation of artefacts. In the present study, we investigate the concept of using a conductive paste electrolyte in a two- electrode system consisting of a substrate and a single counter/reference electrode to evaluate the effect of protective layers, patina and coatings, on bronze. The EIS response of the cell was found to be sensitive to the application of sulphide patina and Palaroid- B72 coating layers on the polished CuSn6 and CuSn12 bronze surface. Protected CuSn12 bronze samples were exposed to a condensing atmosphere with constant humidity for 24 hours alternately in the climatic chamber. The EIS spectra were measured and the numerical values of impedance at 0.1 Hz were used as an indicator of the degree of surface protection by patina or coating. The aim of this work was to evaluate the susceptibility of the surface to corrosion, i.e., to correlate the measurement results with the condition of the surface before, during, and after the adverse effects caused by the uneven coverage by protective layers. For the practical application of this method, seven Austro-Hungarian 2-Heller coins from a private collection were also EIS tested, in pristine state and with a single coat of Palaroid B-72.

bronze ; EIS ; paste electrolyte

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